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Local state estimation and data reconciliation in electrical substations

IP.com Disclosure Number: IPCOM000179512D
Publication Date: 2009-Feb-16
Document File: 5 page(s) / 125K

Publishing Venue

The IP.com Prior Art Database

Abstract

IEC 61850 introduces the concept of a process bus, which is an Ethernet bus connecting the Intelligent Electronic Devices (IEDs) with the merging units (MU) of measurement transformers (current and voltage transformers). This makes current and voltage measurements available to all IEDs of a common process bus. As a result, local state estimation and/or data reconciliation can be performed within the substation. This leads to the following novel applications: - Improved protection through more accurate measurement values. - Improved measurement values to provide to the network control centre: compensate for inherent measurement transformer errors. - Reduce primary equipment cost by removing the need for some measurement transformers (e.g., one current value can be computed from other current values of "connected" CTs). - Improve reliability of the substation automation system in general, as the failure of one measurement transformer can be compensated by computing the missing measurement out of others or as another measurement transformer at another bay can be selected due to network topology. - Alarming on gross measurement transformer (or associated merging unit) failures, i.e., when measurement values diverge so much that data reconciliation cannot correct the values.

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ID CH-0842005

LOCAL STATE ESTIMATION AND DATA RECONCILIATION IN ELECTRICAL SUBSTATIONS

Abstract

IEC 61850 [1] introduces the concept of a process bus, which is an Ethernet bus connecting the Intelligent Electronic Devices (IEDs) with the merging units (MU) of measurement transformers (current and voltage transformers). This makes current and voltage measurements available to all IEDs of a common process bus. As a result, local state estimation and/or data reconciliation can be performed within the substation.

This leads to the following novel applications:
• Improved protection through more accurate measurement values.
• Improved measurement values to provide to the network control centre: compensate for inherent measurement transformer errors.
• Reduce primary equipment cost by removing the need for some measurement transformers (e.g., one current value can be computed from other current values of "connected" CTs).
• Improve reliability of the substation automation system in general, as the failure of one measurement transformer can be compensated by computing the missing measurement out of others or as another measurement transformer at another bay can be selected due to network topology.
• Alarming on gross measurement transformer (or associated merging unit) failures, i.e., when measurement values diverge so much that data reconciliation cannot correct the values.

Background of the invention

Current (CT) and voltage (VT) transformers in an electrical substation provide measurements to the IEDs (Intelligent Electronic Devices), which use these values for protection (of the electrical network) purposes. If the sampling frequency fulfils certain requirements, the values can also be used for data metering purposes. These measurements are usually also forwarded to a network control centre through either a gateway or an RTU (Remote Terminal Unit). As shown in Figure 1, today these measurement transformers are hard-wired with multiple copper wires to the IEDs, which decode the values by means of an analog input board. As a result, if the wiring between any measurement transformer and an IED is cut or if a measurement transformer fails, the protection functions implemented in the IED cannot be executed reliably.

Figure 1: Traditional way of connecting measurement transformers (CTs and VTs) to IEDs.

The international standard IEC 61850 [1] introduces the concept of a process bus, shown in Figure 2, which is an Ethernet bus connecting the IEDs with the merging units (MU) of the measurement transformers (CTs and VTs). Its main goal is to reduce wiring costs (less copper) and simplify engineering. Measurements are sent from the MUs as sampled value streams (which are Ethernet frames). As a result, measurements from several CTs and VTs might be available to multiple IEDs, provided they share the same process bu...